VOLCANIC EPISODES OF THE PHANEROZOIC RECORDED IN THE SEDIMENTARY ROCK RECORD

It has been previously established on the basis of marine tephra occurences that at least three global-scale subaerial volcanic episodes occurred during the Cenozoic. However, it has been not been known whether similar volcanic episodes have occurred in the deep past. An extensive review of the geologic literature on ancient tephra, bentonites, tonsteins, etc. indicates that global volcanic episodes have occurred at various scales from 10 to 30 million years throughout the Phanerozoic. The abundance of tephra at different time scales show clear trends despite preservation biases. These volcanic episodes of the Phanerozoic appear to be coincident with climatic and environmental fluctuations, namely cool modes or continental glaciation. Whether these volcanic episodes can be said to have any causal relationship with global cooling is unclear. Likewise, these large scale volcanic episodes do not appear to have an obvious relationship with Plate Tectonics and Large Igneous Provinces. Regardless of any causal relationships with similarly scaled events, assuming that these volcanic episodes are real global events has yielded a useful model for locating unreported tephra which have been utilized as dating tools in stratigraphic problems.